Recording lamp



March 28, 1933. c PACKARD 1,903,128

RECORDING LAMP Filed March 1, 1929 Y... r .9, K2!!!!llIlll!lllll!llllllllllllllllllllllllllllllllllIllllI!!!lllllllll!!!I!ml!!!I!!!Ill!!!!!!!!!!!!!!!!!!!!!!!!!LZ I & .smmummrlmval 3555-2 f IETfIE E f 16 am Ad m DEIEH'JEIEIE] A TTORNEY Patented Mar. 28 1933 UNITED STATES oiimnns A. raoxann, or nhnms, arms ancoannm mm Application filed larch 1,

This invention relates to sound recording apparatus and it has particular reference to apparat for recording sound on motion picture film or similar hotosensitive material, and the principal ob ect of the invention resides in the provision of means in apparatus as specified for eliminating all movement of elements larger than molecules at sound frequencies and thereby simplify the device and prevent distortion when reproduced.

A further object of the invention resides in the'provision of means for recording a type of record upon photosensitive material, which, due to high contrasts, is easily developed.

The invention further comprehends an apparatus of the character designated, a novel source of illumination which performs an important part in recordin sound in a simple and efficient manner, an through which recording is accomplished without the aid of mechanical means.

With the foregoing objects as paramount, the invention has particular reference to its salient features of construction and arrangement of parts to become manifest as the de scription proceeds, taken in connection with the accompanying drawing wherein;

Figure 1 is an axial sectional view of a lamp constructed according to the present invention, comprised of an isolantite rod having nichrome winding and a metallic tube arranged in parallel relationship therewith in a gas filled transparent tube.

Fi re 2 is a modified form of lamp in which the dark electrode is curved and divided relative to the illuminable electrode.

Figure 3 is a further modification of the lamp in which the dark electrode is curved in different planes relative to the illuminable late. p Figure 4 is one form of apparatus embodying the elements of the present invention showing the relatively disposed lens, mask and photosensitive film.

Figure 5 is another and preferred form of the invention showing the means for affecting variable illumination of one of the lamp electrodes, and focusing a real image thereof on the photosensitive film, and

Figure 6 is a fragmentary piece of the film 1929. Serial No. 343,809.

and sound track, showing an example of the type of record produced by the present invenion.

Among the various methods and systems of recording electrical current waves on light sensitive films, there is one which has a sound track of constant width, but which records the variations of electrical current by directing a ray of light through a slitted mask, and projecting a real image of the slit upon the film with variable intensity. The film, when developed will show a sound track having an infinite variety of transverse shadings denoting sound variations.

This method, while well known to the art, requires that great care be exercised in recording, developing and reproducing, and moreover, it is necessary in recording under this method to select the most perfect film stock and employ many expensive precautions if the relative density of all the degrees of shading are to be maintained. Distortion is almost alwayspresent in the translation of films produced in this manner, since the infinite shadings are usually deformed in the developing and printing operations.

Another form of light sensitive film recording employs a film in which the sound track devoted to the record is partially exposed to a light of substantially constant brilliance while the remainder of the track is unexposed. The variations of the electrical current are recorded by varying the ratio of the exposed width to the unexposed width of the sound track. This system of sound recording is sometimes known as the saw-tooth method due to the appearance thereof on the developed film. This method of recording possesses greater efiiciency in view of the contrasting densities of the sound track, and are more easily developed and printed for the same reason.

The latter method of recording however, necessitated the use of swinging mirrors, shutters or similar mechanical or electromechanical elements vibrating at the frequency of the recorded wave forms.

The mass of such parts, especially at higher frequencies, introduces the distortion com mon to most of the prevailing and well known systems. The present invention affords means by which to eliminate all vibrating mirrors, shutters and the like and permits, at the same time, the use of constant density, variable width record.

Accordingly the invention consists primarily of a lamp of novel and peculiar construction which is capable of recording constant density, variable width records without the use of any moving parts more ponderous than molecules. The lamp, of which several modifications is shown, is designated by the character 1 throughout the several views, and is unique in that the light emitting area varies with changes in the applied voltage. In the preferred form of lamp shown in Figure 5,

the electrode 2 is illuminated over a portion of its surface by current drawn from battery 4. The percentage of electrode illuminated when no recording is being done is determined by the setting of the potentiometer 5, which, under normal conditions, should be made so that the electrode 2 is illuminated for about one half of its useful length.

The lamp 1, as apparent inthe Figures has two electroles, 2 and 3, the latter being herein referred to as the dark electrode, while the other is termed the luminous electrode. Either the luminous electrode 2 or the dark electrode 3, or both should be composed of a material having considerable electrical resistance. A potential gradient is maintained in one or both of these electrodes so that the illumination does not occur instantly over the entire surface of electrode 2 but progresses from the negative to the ositive end of the electrode as the voltage etween it and the electrode 3 is increased. Actual experiments have resulted in the development of the structure shown in Figure 1, which consists of a sealed tube 6 of flawless optical glass evacuated through nipple 6a and filled with neon, helium or similar gases and in which one of the electrodes consists ofa non-conducting cylinder, or electrode 2, hereinbefore referred to as the illuminous electrode, wound spirally with fine resistance wire, while the other or dark electrode '3 is formed by a hollow metallic cylinder. Battery 7 serves to maintain a potential gradient in electrode 2, while battery 4 may be used to maintain a potential difference between the electrodes. Rheostats 9 and 10 control the potential gradients in their respective circuits. Battery 8 in Figure 5 maintains a potential gradient in electrode 3.

The present system of recording employs a mask 11, in which is made a slit 12, so disposed as exemplified in Figures 4 and 5, relative to the lens 13 and film 14 as to allow a real image of the electrode 2 to be focused through the slit 12 onto the film within the margin alloted to the record track 15, as in Figure 6. 1 i .5"

The example shown in Figure 5 clearly illustrates the function of the invention. The light emitted by the electrode 2 is intense but variable, that is to say, the ed e of the illuminous area designated at a in igure 5 moves relative to the negative and positive ends of the electrode in accordance with the variations and modulations of sound impinged upon the diaphram of the microphone 16.. The dotted lines indicate the light rays emitted by the electrode 2, through the double convex lens 13 and converging at a point beyond the mask 11 to a focus on the film record track 15, at b, which represents a real image of the electrode 2.

Obviously, as the sound waves fluctuate, the illuminated area a on the electrode 2 accordingly fluctuates, and its image being projected upon the exposed edge of the film 14, a permanent sound record is produced, which, due to the extreme contrasts in the exposed and unexposed portions of the sound track, is easily developed and printed and when ready for translation, may be reproduced with minimum distortion.

When sounds impinge on the diaphragm of the microphone 16, the current in the microphone circuit is modulated and may be amplified by vacuum tubes, (not shown). This modulated current is passed through the primary of the transformer 17, and the voltage generated in the secondary of this transformer is added to or subtracted from the voltage of the battery 4, due to their series connection. The algebraic sum of the battery voltage and the voltage across the secondary of the transformer 17 is impressed upon the terminals of lamp 1, causing the illumination to covera larger or smaller area of the illuminable electrode 2. By means of the lens 13, previously mentioned. a real image of the electrode 2 is focused onto the film record track 15, through aperture 12 in the mask 11. In some cases. it is possible to eliminate the gradient batteries 7 and 8 by use of a curved electrode as shown in Figure 2. It has been found that with all types of lamps, and espeeially with this type, satisfactory operation may require the use of a grounded screen surrounding either the lamp or the entire apparatus.

The foregoing description is calculated to define an embodiment of the invention hereinafter claimed, that is. a lamp comprising an evacuted transparent tube, and filled with suitable gases and containing electrodes, one or both of which have considerable electrical resistance. with means for passing a direct current through the electrodes to maintain a potential radient. and means for applying a modulated voltage between the electrodes for the purpose of causing the area of the source of illumination to vary in accordance with the modulation of the applied voltage. It should be herein understood that the invention is not limited to the specific arrangement, number or shape of the electrodes employed, nor the means for transmission of potential gradient.

The objects of the present invention are wellin evidence and any and all good and useful things and purposes achieved or secured through the instrumentalities of this invention are deemed to be well within the category of its objects.

What is claimed is:

A lamp of the character described including a gas filled, transparent tube having a pair of electrodes therein, one of which consists of a spiral winding of fine resistance wire closely adjacent and parallel to the other electrode, means for maintaining potential gradient in said illuminable electrode and means connecting said electrodes for maintaining a potential difi'erence between the same.

In testimony whereof I aflix my signature.

CHARLES A. PACKARD; 

